Super JX

Ten years ago, I decided to upgrade my JX10, the idea being to add PWM. This turned into a considerable hobby project... the sound board code had to be modified, as well as the assigner code. While the former is pretty well written, the assigner code on the JX10 and the MKS70 is not particularly pretty. It is actually impossible to upgrade, so I started to rewrite it from scratch. Today, I am proud to announce the availability of this rewritten firmware, which should give an entire new experience and life to our loved JX synthesizers. A JX8P version is now available !

I get often asked if this project is still alive: yes, it is still going strong in 2023!


The project continues with the PWM hardware mods. But unlike the assigner rewrite, adding PWM requires surgery to the sound boards, while the assigner rewrite is simply an eprom change.

A new PWM kit is available, it replaces the 4 counter chips by a little board with FPGA. No more ugly wiring required, just desoldering/soldering. See the new page here.

A 16-banks M-1024C cartridge has been developed too, and is available (in limited quantity). See this page. Since cartridges are expensive and hard to find, I designed a new module which replaces the assigner eprom with a flash chip, providing 16 or 32 banks of patches/tones and midi firmware upgrade. See this page for more info.

Pasted Graphic

For PWM, see PWM kit pictures gallery, kit install manual download section and PWM tone parameters description. Excellent install guide by Guy available here!

A display replacement is now available, using a Noritake GU280x16 display. Website and youtube video here.

New features

In a nutshell, the rewrite provides :
New midi implementation
  • each parameter is now OFF/RECV/SEND/ON, allowing fine control of what gets sent and what is filtered.
  • sysex support : allow edition of patch, tone A and tone B individually. (No need for M64 cartridge)
  • midi cc support : allow edition of all tone parameters (each tone separately or both tones) with midi cc.
  • fast bulk dump/load : 4-5 seconds to dump everything. Can dump to/from cartridge and internal memory.
  • edition of parameters (patch and tones) sends sysex, so all editions can be sequenced. PG800 is also supported here, so editions made from the PG800 can also be sequenced.
  • copy from/to cartridge to create a full backup of the internal memory (all settings are now copied to the cartridge or restored from it)
Controls C1 and C2 enhancements
  • any tone parameter (from tone-A, tone-B or both at the same time) can be assigned to C1 or C2
  • any arpeggiator parameter can be assigned to C1 or C2
  • C1 and C2 can be used, in tone edit mode, to modify upper/lower tone parameter. This allows quick editing of tones for those who don’t have a PG800.
  • C1 or C2 ban be used to simulate aftertouch.
Arpeggiator (JX10 and now MKS70)
  • 8 arpeggiators “patches”
  • internal or external synchronization
  • supports up, down up/down, played and random notes ordering
  • various arpeggio types
  • velocity setting (fixed or played)
  • note duration (1-15 or legato)
  • use lower split point to control which notes are arpeggiated
  • Demo on youtube (beta version)
Chord mode
  • On JX10, chord mode has been added.
PG800 and mini-PG800 support
New display options
  • control whether updates from sysex, pg800 or controllers are displayed temporarily on-screen
Compatibility mode
  • allows to disable new features for full compatibility with old software (for example, sysex changes made to tone A can be redirected to the currently selected tone, etc...)
Test modes
  • test hardware controllers (voices, A/D controllers (aftertouch, bender, C1/C2), keyboard)
  • test memory chips
For MKS70 owners, please note that the MONO mode (one voice per midi channel) is NOT SUPPORTED in this release.


The new firmware 3.0x is available! It is delivered as a new eprom (replacement for Roland “ROM A”) or as a flash module. (For JX10 owners, check your sound board roms. If they are older than 2.0, they won’t support 12 semi-tones for the bender. For MKS70, the very old 1.03 is buggy too) PWM kits are now available again!!!. Please send your request to

Manuals and Demos

The eprom replacement guide (for JX10 and MKS70) and an updated manual (updated Nov 2016) are available in the download section. Nice 3.x install video. Another one (with display upgrade).

Release notes

Please check this page.

PWM kit!

The next step involves replacing the 8031 CPU of the sound boards, with a new firmware (“ROM B” and “ROM C”). This provides new envelopes, new LFO, and several other new parameters to control the tones. The PWM kit used to require adding 2 daughter boards, each connected with 36 wires. This is now replaced by a digital pwm kit which involves removes 5 chips on each sound board, making it easier to install. Details here.


Users undertaking this DIY project need to have experience in electronics, mains appliance wiring and testing. No liability can be undertaken by the author for the design, installation or damage to the instrument.

History of the project

Can be found here. Lots of discussions regarding the new firmware on this forum thread. Demo on youtube.